Isomerization and aggregation of 2-(2-(2-hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-dione: recent evidences from theory and experiment

The title compound potentially can exist as four isomers in solution. Recently Lycka has proposed a protocol for distinguishing two of them based on ¹⁵ N NMR. This approach has been confirmed theoretically, in the current study, and further developed into a logical scheme that allows the existence of each of the isomers to be proven in solution. The experimental data, obtained by NMR and UV–Vis spectroscopy, have shown that the studied compound exists as a mixture of two solvent stabilized isomers in diluted solutions of dimethyl sulfoxide. However, the concentration effect also plays a substantial role allowing formation of linear aggregates as the X-ray analysis and theoretical calculations show.